Sujet : Re: CCFL transformer
De : jjSNIPlarkin (at) *nospam* highNONOlandtechnology.com (John Larkin)
Groupes : sci.electronics.designDate : 27. Apr 2024, 04:34:19
Autres entêtes
Organisation : Highland Tech
Message-ID : <60po2j567ogmhdvg3hte0kjlkn7eq0vqpj@4ax.com>
References : 1 2 3 4 5
User-Agent : Forte Agent 3.1/32.783
On Sat, 27 Apr 2024 02:17:23 +0200, Klaus Vestergaard Kragelund
<
klauskvik@hotmail.com> wrote:
On 25-04-2024 09:02, Bill Sloman wrote:
On 24/04/2024 3:10 pm, Bill Sloman wrote:
On 24/04/2024 12:25 pm, John Larkin wrote:
On Wed, 24 Apr 2024 01:57:36 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:
>
Hi
>
I need a low distributed capacitance winding transformer, for a HV
step-up function (3.5kV)
>
I am zeroing in on similar concept as CCFL transformers with
sectionalized bobbin.
>
For example:
>
https://www.coilcraft.com/en-us/products/transformers/power-transformers/ccfl-transformers/fl/
>
Possibly using Triple Insulated Wire to create some distance between
the
individual turns.
>
Not many sells CCFLs these days.
>
Guess I will keep it alive....
>
Can you use a C-W multiplier?
>
For low current, you can do resonant tricks too.
>
It's easier to use a voltage doubler or tripler that it is to find a
multi-section former off-the shelf. The occasional high voltage power
supply that I've dismantled clearly used proprietary formers, as do
the Coilcraft parts
>
I suppose one could use self-bonding wire to make a series of
self-supporting pancake windings, but I've never heard of anybody
doing it.
>
The Baxandall configuration is definitely a resonant trick, and copes
with the interwinding capacitance by resonating it with the winding
inductance.
>
There's nothing "low current" about it, but if you are working at
higher currents and powers you can justify even more elaborate
switching arrangements.
>
http://sophia-elektronica.com/Baxandall1959JM.pdf
>
Jim Williams talked about it a lot - application notes AN45, AN49,
AN51, AN55, AN61, AN65 - but described it as a "a current driven Royer
inverter" which is simply wrong.
>
MOSFETs work better as switches than bipolar transistors, and don't
seem to "squeg".
The Coilcraft data sheets don't say anything much about the resonant
frequencies of their transformers - except "The FL Series of
transformers is designed for use in cold cathode fluorescent lamp (CCFL)
power supplies at operating frequencies up to 100 kHz" where the "up to
100kHz" gives them a lot of wriggle room.
A primary inductance of around 50uH with a 100:1 step-up implies a 0.5H
secondary inductance. 10pF parallel capacitance would give a 71kHz
resonant frequency, which is less than 100kHz.
Of course once you have one of the Coilcraft parts you can measure the
resonant frequency.
>
Measurement:
>
https://www.electronicsdesign.dk/tmp/FL2015-4D_primaryL.png
>
FL2015-4D, primary inductance is 43uH. Resonance is 332kHz, reflected
capacitance to primary is 5nF. Reflected to secondary 100mH is 2.3pF
Leakage inductance?